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. Quarterly Groundwater Monitoring Report Frontier Transportation 4199-068 February 11, 1999 ' Naphthalene, 79 ug/L as n-Pro ylbenzene, 500 as l 2 4-Trimeth lbenzene p � � Y > and 90 µg/L as 1,2,5-Trimethylbenzene. ' MW-4 -! 7µg/L as Naphthalene. • MW-5 -4 No detectable concentrations of analytes. • MW-6 -4 6µglL as Acetone. ' MW-7 4 No detectable concentrations of analytes. 5.0) CONCLUSIONS AND RECOMMENDATIONS Bas n Based o groundwater sample analysis results, the dissolved petroleum hydrocarbons appeared to be localized near the former tanks location and monitoring well MW-3 in shallow groundwater, however, recent data suggests that this small dissolved plume may be migrating west. Groundwater collected from monitoring wells MW-2, MW-5, MW-6, and MW-7 identified ' low level to no detectable concentrations of petroleum dissolved hydrocarbons (TPH-d, TPH-g, BTEX, and MTBE) which supports that the dissolved phase plume is confined to the site to the east, north and south. Groundwater collected from monitoring well MW-3 identified an attenuation in dissolved petroleum hydrocarbon concentrations since the previous monitoring episode, yet monitoring wells MW-I and MW-4 located down gradient of MW-3 identified an increase in dissolved petroleum hydrocarbon concentrations. The dissolved phase plume appears to be migrating from MW-3. The shallow groundwater beneath the site is designated as non- beneficial use. BEII recommends that quarterly groundwater monitoring continue at the site until constant or decreasing dissolved petroleum hydrocarbon concentrations are observed. In addition, BEII recommends two groundwater draw down episodes from monitoring wells MW-1, ' MW-3, and MW-4 to keep the dissolved plume contained to the site boundaries and prevent further possible migration of the dissolved plume. Groundwater samples will be analyzed for BTEX using EPA method 8020, TPH-g and TPH-d using EPA method 8015m, and oxygenates using EPA method 8260 in all future monitoring episodes as directed by the PHS/EHD. In addition, BEII will conduct a survey of domestic, municipal, agricultural, industrial and any other wells within a 2,000 foot radius from the site and mark the well locations on a scaled map as ' directed by the PHS/EHD. Any known construction details of these wells (if any) will be submitted along with the influence of pumping from these wells (if any). 4